Recently, CRLH (composite right/left-handed) transmission line apparatuses are studied. Conventional composite right/left-handed transmission line apparatuses propagate both a forward wave and a backward wave. In the forward wave (right-handed mode) propagation, the transmission power and the phase flow of electromagnetic waves have the same direction. In the backward wave (left-handed mode) propagation, the transmission power and the phase flow have opposite directions. These two propagation characteristics are selectively changed depending on their different operating bands. On the other hand, in Patent Literature 1, Non-Patent Literatures 1 to 3, and so on, one of the inventors of the present application proposed a nonreciprocal transmission line apparatus operable in a single operating band capable of both forward propagation in the right-handed mode and backward propagation in left-handed mode.
FIG. 117 is a perspective view of a configuration of a conventional nonreciprocal transmission line apparatus as disclosed in Patent Literature 1. The nonreciprocal transmission line apparatus of FIG. 117 comprises:
(a) a substrate, the substrate comprising: a ferrite substrate 10F, a dielectric substrate 10, and a ground conductor 11, the ferrite substrate 10F having a magnetization Ms due to its spontaneous magnetization or an external magnetic field in a direction perpendicular to a surface of the substrate, the dielectric substrate 10 made of, for example, glass epoxy resin or the like, the ferrite substrate 10F and the dielectric substrate 10 connected side by side along a boundary portion between them, and the ground conductor 11 provided on the back surfaces of the ferrite substrate 10F and the dielectric substrate 10;
(b) a microstrip line 12A formed on the boundary portion of the substrate;
(c) a plurality of capacitors C, each connecting a pair of adjacent strip conductors 12 of a plurality of strip conductors 12, the plurality of strip conductors 12 forming a microstrip line 12A; and
(d) a plurality of short-circuit stub conductors 13, each connecting a strip conductor 12 to the ground conductor 11.
Thus, the nonreciprocal transmission line apparatus of FIG. 117 includes a cascade connection of unit cells of the transmission line between ports P1 and P2, each of the unit cells having a series branch circuit including an equivalent capacitive element, and a shunt branch circuit including an equivalent inductive element, each of the unit cells having gyrotropic characteristic by being magnetized in a magnetization direction different from a propagation direction of a microwave, each of the unit cells having an asymmetric structure with respect to a plane composed of the propagation direction and the magnetization direction, each of the unit cells being set with a propagation constant and an operating frequency on dispersion curves representing a relation between the propagation constant and the operating frequency, so as to have nonreciprocal phase characteristics with different forward and backward propagation constants.